Magnetotransport and magnetic domain structure in compressively strained colossal magnetoresistance films

Abstract

We have studied the magnetoresistance ͑MR͒ of compressively strained La 0.7 Sr 0.3 MnO 3 ͑LSMO͒ films in various magnetic states in order to understand the role of magnetic domain structure on magnetotransport. In thin films of LSMO on ͑100͒ LaAlO 3 , the perpendicular magnetic anisotropy results in perpendicularly magnetized domains with fine scale ϳ200 nm domain subdivision, which we image directly at room temperature using magnetic force microscopy. The main MR effects can be understood in terms of bulk colossal MR and anisotropic MR. We also find evidence for a small domain wall contribution to the MR, which is an order of magnitude larger than expected from a double exchange model.The doped perovskite manganites have received an enormous amount of attention recently because they exhibit colossal magnetoresistance ͑CMR͒ and may be half metallic, with complete spin polarization at the Fermi level. For these reasons, they may find important uses in magnetoresistive devices, such as magnetic random access memory and sensors. As has been found in magnetoresistive devices based on transition metal ferromagnets, controlling the electronic transport and magnetic properties of these materials in thin film form will be essential to applications. Experimentally, the magnetic and transport properties of colossal magnetoresistance materials have been shown to be highly sensitive to microstructure as well as lattice distortions both in thin film and bulk form. Many groups have shown that properties such as Curie temperature, resistivity and magnetoresistance effect are extremely sensitive to chemical and hydrostatic pressure as well as lattice mismatch with an underlying substrate.1-11 Studies of bulk polycrystalline pellets, thin films of varying polycrystallinity and isolated grain boundaries have shown that the magnetoresistance is profoundly affected by transport across grain boundaries. 2,12,13 Magnetic domain structure may also to lead to distinctive magnetotransport effects in thin films. Mathur et al. report that the measured resistivity of a magnetic domain wall is four orders of magnitude larger than that predicted by a simple double exchange picture.14 Wang et al. have also suggested that large low field magnetoresistance ͑MR͒, in ultrathin compressively strained doped manganite thin films, may be due to domain wall scattering.9 In order to address these questions in LSMO, we have prepared in-plane compressively strained films of LSMO on ͑001͒ LAO (aϭbϭc ϭ3.79 Å) substrates using pulsed laser deposition.9 These films naturally split into stripe domains with length scales set by the strain and film thickness. This enables us to study the effect of magnetic microstructure on MR in a systematic manner. In this letter, we have investigated the magnetics and magnetotransport of epitaxial La 0.7 Sr 0.3 MnO 3 ͑LSMO͒ films. The main MR effects can be explained by CMR and anisotropic MR. We also find evidence for a small domain wall ͑DW͒ contribution to the MR, which is an order of magnitude larger than expected based ...

Superconducting and normal-state interlayer exchange coupling inLa0.67Sr0.33MnO3−YSenapati1, Budhani2 2005Phys. Rev. B360350View full textAdd to dashboardCite

“…The behavior of magnetization in LSMO films deposited on LAO is quite different. The preferred direction of magnetization is perpendicular to the film plane in this case 21,30,31 .…”

“…In addition, LaAlO 3 is a heavily twinned material. Since both these factors are known to affect magnetic anisotropy of LSMO 21 and superconducting properties of YBCO 22 , intrinsic behavior of FM-SC-FM structure is likely to get masked by such stress and interface related effects. Further, the interface related non-intrinsic behavior is likely to get accentuated in superlattices due to the presence of a large number of interfaces in such structures.…”

Magnetic domain structure of La0.7Sr0.3MnO3 thin-films probed at variable temperature with scanning electron microscopy with polarization analysis

“…In (b) an integrated Gauss function has been fitted to a line scan across a domain wall, revealing a transition region of 35±3 nm, which compares favourably with estimates of the domain wall width in this material (∼ 30 − 55 nm 22,23 ). Furthermore, it can be inferred that a largely four-fold anisotropy exists in the films, as schematically indicated by the arrows in enlarged images of panel (a).…”

Pulsed laser deposition of La1−xSrxMnO3: thin-film properties and spintronic applications

“…Because strain control in thin LSMO films is vital for obtaining optimal properties, the effects of strain have been studied extensively [30][31][32] Other factors that control the magnetic and electrical transport properties of LSMO are film composition, oxygen stoichiometry and crystal orientation [34][35][36][37][38]. The composition and oxygen content mainly affect the saturation moment and the transition temperature, whereas lattice strain and film texture can also induce magnetic anisotropy [39,40]. Moreover, LSMO films with a polycrystalline texture can exhibit large LFMR and a large dielectric constant due to the presence of high and low angle grain boundaries.…”